# Cos2θ to sinθ? Identity conversions

• November 28th 2012, 07:56 PM
whittwhitt
Cos2θ to sinθ? Identity conversions
How to find cos2θ if sinθ = 2?

How to find cosθ if sin2θ = 3?

Both lie in quadrant I. I'm unsure how to convert from one identity to the other ...
• November 28th 2012, 08:03 PM
jakncoke
Re: Cos2θ to sinθ? Identity conversions
How can $sin(\theta) = 2$ if its maximum value is 1.
• November 29th 2012, 04:15 AM
skeeter
Re: Cos2θ to sinθ? Identity conversions
In this post ...

http://mathhelpforum.com/trigonometr...equations.html

...you were requested to post specific problems rather than cryptic references to double angle problems. Now it seems you're making up stuff, because you really don't know what you're doing.

Post a specific problem from a text or as given by your instructor.
• November 29th 2012, 06:42 AM
topsquark
Re: Cos2θ to sinθ? Identity conversions
Quote:

Originally Posted by whittwhitt
How to find cos2θ if sinθ = 2?

How to find cosθ if sin2θ = 3?

Both lie in quadrant I.

Yes. Impossible. $-1 \leq sin(\theta) \leq 1$. For any angle in any quadrant.

Quote:

Originally Posted by whittwhitt
I'm unsure how to convert from one identity to the other ...

You have now got several references to the double angle formulas. Please use them and show us what you've got.

But please let us know what the actual problem statements are. You have been asked to clarify a question before.

-Dan